Various techniques have been used in the prior art to record, transmit and display three-dimensional (“3-D” or stereoscopic) still or motion images for broadcasting, entertainment, scientific research, engineering design, medical or military applications. To generate 3-D images, many such conventional techniques call for the use of two camera systems, whereby two different images are taken from slightly different camera angles and locations, so as to simulate the process by which depth is perceived by a pair of eyes separated by the inter-pupil distance. The two images are then superimposed, either before or after transmission, and finally displayed on a display apparatus such as a television or screen. Conceivably, the two superimposed images are somehow “separated” in the eyes of the viewer, such that one eye sees only one image while the other eye sees only the other image, and as a result an illusion of depth is created by simulating normal human vision.
A popular conventional technique for generating and displaying 3-D images is the anaglyphic 3-D process. Essentially, this technique uses color filters, in the form of a pair of colored glasses worn by the viewer, to separate the two images respectively presented to the right and left eyes. Simultaneously, watching the breakdown images with the right eye and the left eye can give the image a three-dimensional look. An example of the anaglyphic process is described in U.S. Pat. No. 3,697,679, entitled “Stereoscopic Television System” and issued to T. Beard, et al.
Another conventional process is the so-called Polaroid process, in which the right and left images are separated by the use of polarized light filters. The right eye image is projected onto a screen through a polarizing filter rotated 45° to the right of vertical, while the left eye image is projected onto the same screen through a polarizing filter rotated 45° to the left of vertical. Similarly, polarized filters are placed in front of each of the eyes of the viewer, causing the proper image to be transmitted to each eye.
A more recent technique for viewing 3-D images is to make the viewer wear a pair of spectacles incorporating liquid crystal shutters. The image on the display alternates between a right-eye view and a left-eye view in a time-multiplexed fashion. If the image is synchronized with the spectacle shutters at a sufficient rate, the viewer can see a flicker-free stereoscopic image. Alternatively, a liquid crystal shutter may also be disposed in front of a display apparatus while the viewer uses a pair of polarized glasses to view the images. As an example, this is disclosed in U.S. Pat. No. 6,252,624 B1, entitled “Three Dimensional Display” and issued to K. Yuasa, et al.
The right and left perspective images of a 3-D video display system may also be spatially multiplexed during the image generation process to produce a multiplexed composite image. During the image display process, the visible light associated with the right and left perspective image components of the composite image are simultaneously displayed, yet with spatially different polarizations. This perspective image blocking or selective viewing process is typically achieved by the use of spectacles incorporating a pair of spatially different polarizing lenses. Alternatively, micropolarizers may be mounted onto the display surfaces to emanate the polarized light of spatially multiplexed images.
Another prior-art 3-D image display system makes use of the spectral properties of both right and left perspective color images and ensures that the right eye of the viewer sees only the right perspective color images and the left eye of the viewer sees only the left perspective color images of a 3-D scenery. As an example, U.S. Pat. No. 4,995,718, entitled “Full Color Three-Dimensional Projection Display” and issued to K. Jachimowicz, et al., teaches a display system that includes three monochrome image sources and utilizes image polarization for color multiplexing. As another example, U.S. Pat. No. 6,111,598, entitled “System and Method for Producing and Displaying Spectrally-Multiplexed Images of Three-Dimensional Imagery for Use in Flicker-Free Stereoscopic Viewing Thereof” and issued to S. Faris, discloses another method and apparatus for producing and displaying pairs of spectrally multiplexed grayscale or color images of a 3-D scenery.
It is clear from the above that central to current 3-D imagery systems is display equipment and methods that are capable of expressing high-quality stereoscopic images in accordance with any one or more of the stereoscopic imaging techniques known to those skilled in the art, including, without limitation to, those techniques described above. Aside from displays based on the conventional cathode-ray tube (“CRT”), various flat panel display equipment and methods have been known, including those based on light emitting diode (“LED”), electroluminescence (“EL”), field emission (“FE”), vacuum fluorescence, AC or DC plasma and liquid crystal displays (“LCD”). Many of these techniques have been applied to stereoscopic imagery systems, each, to a more or less extent, successfully.
Another recent display technology, the electrophoretic display (“EPD”), appears promising but has not been adapted for 3-D imagery systems and applications. An EPD is a non-emissive device based on the electrophoresis phenomenon in which charged pigment particles suspended in a dielectric solvent are influenced by a pair of electrodes. An EPD typically comprises a pair of opposed, spaced-apart, plate-like electrodes, with spacers predetermining a certain distance between the electrodes. At least one of the electrodes, typically on the viewing side, is transparent. The viewing-side plate is usually the top plate. In a passive-type EPD, row and column electrodes on the top and bottom plates respectively are used to drive the displays, whereas an array of thin film transistors (“TFT”) on the bottom plate and a common, non-patterned transparent conductor plate on the top plate are required for the active type EPDs. Typically, an electrophoretic fluid, comprising a colored dielectric solvent and charged pigment particles dispersed therein, is enclosed between the two electrodes.
An EPD operates as follows. A voltage difference is imposed between the two electrodes, causing the charged pigment particles to migrate to the plate of a polarity opposite that of the particles. By selectively charging the two plates, the color shown at the top (transparent) plate can be either the color of the solvent or the color of the pigment particles. Reversal of the plate polarity will cause the particles to migrate in the opposite direction, thereby reversing the color shown at the top plate. Furthermore, intermediate color density (or shades of gray) due to intermediate pigment density at the transparent plate may be obtained by controlling the plate charge through a range of voltages.
In addition to the typical reflective mode, U.S. Pat. No. 06,184,856, entitled “Transmissive Electrophoretic Display with Laterally Adjacent Color Cells” and issued to J. G. Gordon II, et al., discloses a transmissive EPD comprising a backlight, color filters and substrates with two transparent electrodes. Each electrophoretic cell sandwiched between the two electrodes serves as a light valve. In the collected state, the particles in the cell are positioned to minimize the coverage of the horizontal area of the cell and allow the backlight to pass through the cell. In the distributed state, the particles are positioned to cover the horizontal area of the cell and scatter or absorb the backlight. The major disadvantage of this EPD device is that the operation of its backlight and color filters consumes a great deal of power, an undesirable feature for hand-held devices such as PDAs (personal digital assistants) and e-books.
EPDs of different pixel or cell structures have been reported in the prior art; for example, M. A. Hopper and V. Novotny, in IEEE Trans. Electr. Dev., 26(8):1148-1152 (1979), teaches a partition-type EPD; U.S. Pat. No. 5,961,804, entitled “Microencapsulated Electrophoretic Display” and issued to J. Jacobson, et al. and U.S. Pat. No. 5,930,026, entitled “Nonemissive Displays and Piezoelectric Power Supplies Therefor” and issued to J. Jacobson, et al., disclose a number of microencapsulated EPD devices. U.S. Pat. No. 3,612,758, entitled “Color Display Device” and issued to P. F. Evans, et al., discloses another type of EPD wherein the electrophoretic cells are formed from parallel line reservoirs or microgrooves. Each of these devices, however, has its problems as noted below.
In a partition-type EPD, there are partitions between the two electrodes for dividing the space into smaller cells to prevent undesired movements of the particles such as sedimentation. However, difficulties are encountered in the formation of the partitions, the filling of the display with the fluid, the enclosure of the fluid in the display and the separation of electrophoretic fluids of different colors or polarization properties from each other. A full color or 3-D image presentation is thus impossible because of the lack of a mechanism to eliminate the undesirable cross-talk due to intermixing of components among the cells.
The use of parallel line reservoirs such as microchannels, microgrooves or microcolumns to form the EPD device has the problem of undesirable particle sedimentation or creaming along the channel or groove direction. The pixel dimensions, particularly the length of the channels or grooves, are too long for an acceptable polarization or color separation for 3-D image or full color presentations, respectively. In addition, the lack of a seamless, air-pocket-free and continuous sealing process to enclose the electrophoretic fluid without undesirable intermixing or cross-talk makes the 3-D image or roll-to-roll manufacturing extremely difficult.
The prior-art microencapsulated EPD devices have a substantially two-dimensional arrangement of microcapsules, each having therein an electrophoretic composition of a dielectric fluid and a dispersion of charged pigment particles that visually contrast with the dielectric solvent. Typically, the microcapsules are prepared in an aqueous solution and, to achieve a useful contrast ratio, have a relatively large size (i.e., 50-150 microns). This large microcapsule size results in a poor scratch resistance and a slow response time for a given voltage because of the relatively large inter-electrode gap dictated by the relative large capsules. Also, the hydrophilic shell of microcapsules prepared in an aqueous solution typically results in sensitivity to high moisture and temperature conditions. To embed the microcapsules in a large quantity of a polymer matrix may obviate these shortcomings, but only at the expense of an even slower response time and/or a lower contrast ratio. To improve the switching rate, a charge-controlling agent is often needed in this type of EPD. However, the microencapsulation process in an aqueous solution imposes a limitation on the type of charge-controlling agents that can be used. Other drawbacks associated with the microcapsule system include poor resolution and poor addressability for color or 3-D applications because of its large capsule size and broad size distribution.
A new EPD apparatus and method was recently disclosed in the following co-pending U.S. patent applications: U.S. Ser. No. 09/518,488, filed on Mar. 3, 2000 (corresponding to WO01/67170), U.S. Ser. No. 09/759,212, filed on Jan. 11, 2001, U.S. Ser. No. 09/606,654, filed on Jun. 28, 2000 (corresponding to WO02/01280) and U.S. Ser. No. 09/784,972, filed on Feb. 15, 2001, all of which are incorporated herein by reference. This new EPD comprises individually sealed cells formed from microcups of well-defined shape, size and aspect ratio. Each such cell is filled with charged pigment particles dispersed in a dielectric solvent.
The above-described sealed microcup structure enables a format flexible and efficient roll-to-roll continuous manufacturing process for the preparation of EPDs. For example, the displays can be prepared on a continuous web of conductor film such as ITO/PET by (1) coating a radiation curable composition onto the ITO/PET film, (2) forming the microcup structure by a microembossing or photolithographic method, (3) filling the microcups with an electrophoretic fluid and sealing the filled microcups, (4) laminating the sealed microcups with the other conductor film and (5) slicing and cutting the display to a desirable size or format for assembling.
One advantage of this EPD design is that the microcup wall is in effect a built-in spacer to keep the top and bottom substrates apart at a fixed distance. The mechanical properties and structural integrity of microcup displays are significantly better than any prior-art displays including those manufactured by using spacer particles. In addition, displays involving microcups have desirable mechanical properties including reliable display performance when the display is bent, rolled or under compression pressure from, for example, a touch screen application. The use of the microcup technology also eliminates the need of an edge seal adhesive, which would limit and predefine the size of the display panel and confine the display fluid inside a predefined area. A conventional display prepared by the edge sealing adhesive method will no longer be functional if the display is cut or a hole is drilled through the display, because the display fluid would leak out. In contrast, the display fluid within a sealed microcup-based display is enclosed and isolated in each cell. Such a sealed microcup-based display may be cut to almost any dimensions without the risk of damaging the display performance due to loss of display fluids in the active areas. In other words, the microcup structure enables a format flexible display manufacturing process, whereby a continuous output of displays may be produced, first in a large sheet format and then cut to any desired size and format. The individually sealed microcup or cell structure is particularly important when cells are filled with fluids of different specific properties such as colors, polarization, retardation and switching rates. Without the microcup structure and the seamless sealing processes, it would be very difficult to prevent the fluids in adjacent areas from intermixing or being subject to cross-talk in applications such as full color and 3-D presentations.
With recent progresses in other elements of the 3-D imagery system (e.g., digital still and video cameras for recording the images, better algorithms for processing the images, and better image compression for transmission of the images), there is an urgent need in the art for displays that (1) have attributes such as greater format and size flexibility, better image quality including wider viewing angles, better sunlight readability, lower power-consumption and lower manufacturing cost, (2) are light-weight, thin and flexible and (3) are compatible with and adaptable for 3-D imagery systems and applications.